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    <title>Document</title>
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    <script>
        var a = 1;
        var b = a-- + --a; //结果为0,首先直接--a得到0然后0+0(即a--优先级较高大于+)
        document.write(b);
        var c = NaN == NaN; //结果未false NaN不等于任何数包括他自己
        document.write(c);
    </script>
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